The present invention relates to a lockable closure for a threaded conduit.
As used herein, the term "threaded conduit" includes any hollow structure adapted to contain a fluid which structure has an opening and threads surrounding such opening.
In numerous fluid handling and storage applications, it is desirable to seal the opening of a threaded conduit with a closure which cannot readily be removed by unauthorized persons. For example, when gas utility service to a building is temporarily disconnected, the pipe leading from the gas main into the building ordinarily is left in place but is capped or plugged with a lockable closure having features which impede removal of the closure by unauthorized persons and thus impede access by unauthorized persons to the gas contained in the pipe and in the main.
One form of lockable closure which has been utilized prior to the present invention is the plug sold by E. J. Brooks Co. of Newark, N.J. This plug includes an element having male pipe threads, such threaded element having a boss protruding from an end face coaxially with the threads and a hexagonal bore in the boss. A shield is mounted to the boss of the threaded element for rotation on an axis coincident with the axis of the threads. The shield has a hexagonal bore which is alignable with the hexagonal bore of the threaded element. A hexagonal lug is slidably mounted in the bore of the threaded element, and a spring is provided which biases the lug towards a retracted position in which the lug does not protrude from the boss. The lug and the boss are concealed by the shield; a key may be inserted through a small hole in the shield to engage the lug and pull it to an extended position in which a portion of the lug lies in the hexagonal bore of the threaded element and another portion lies in the hexagonal bore of the shield so that the threaded element is connected to the shield for rotation therewith.
When the threaded element is engaged in the female threads of a threaded conduit, only an end face of the threaded element is exposed, the threaded surfaces of the threaded element being concealed by the conduit. Therefore, it is difficult to directly engage the threaded element for rotation and disengagement from the conduit. Although the shield can readily be engaged and rotated, rotation of the shield will not produce rotation of the plug when the lug is in the retracted position. An authorized person in possession of the proper key can disengage the closure from the conduit by moving the hexagonal plug to its extended position to couple the threaded element to the shield for rotation therewith and rotating the shield.
A corresponding cap for conduits having male threads is also sold by E. J. Brooks Co. This cap is similar to the plug described above except that the threaded element has female pipe threads instead of male pipe threads and the shield has a skirt which coaxially surrounds the threaded element.